Solar ultraviolet radiation (UV) is a ubiquitous environmental hazard causing cutaneous inflammation, immune modulation, premature aging of skin and hundreds of thousands of skin cancers each year. Despite its importance to the health of society the mechanism by which UV induces most photobiological effects is poorly defined. Little attention has been paid to the role of membrane constituents in the mediation of UV-induced damage. This is in spite of evidence suggesting that UV damage results in stimulation of processes analogous to changes induced by membrane active agents - hormones, growth factors and chemical tumor-promoters - known to act through a cascade of membrane second messenger signals. The overall objective of these proposed studies is to examine the effect of UV on membrane messenger system metabolism in human epidermis. Previous studies have revealed that UV irradiation of cultured human keratinocytes induces phospholipase activation and eicosanoid production; alters cell growth and differentiation; causes inhibition of binding of epidermal growth factor (EGF) to its receptor (EGFR); and up regulates protein kinase C activity (PKC). This proposal will focus on the mechanism of, and effect of, UV- induced EGFR and PKC modulation. We will determine: a) The site of UV-induced phosphorylation of EGFR and assay the effect of inhibitors of protein synthesis and mRNA synthesis, inhibitors of PKC and EGFR kinases, and inhibition of cytokines, on UV- induced inhibition of EGF binding and EGFR phosphorylation, and the effect of UV on oligomerization of EGFR in intact cells and membrane preparations; b) UV-induced EGFR-TK phosphorylation of phospholipase C (PLC gamma)and GTPase activating protein (GAP); c) The effect of inhibitors of protein and mRNA synthesis on UV-induced PKC activity and content, the effect of UV on translation and inhibitory protein of PKC; and UV-induced PKC gene expression; d) UV-induced phosphorylation of specific PKC substrates - EGFR, MARKS and Mac MARKS. Delineation of the effect of UV on membrane messenger system metabolism of human keratinocytes should yield insight into the role played by such effects on the overall tissue response of human skin to sunlight, extending our knowledge of how UV induces deleterious effects in normal skin and positive effects in diseased skin as occurs with phototherapy of psoriasis.